NASA’s Aqua satellite captured this natural-color image on January 16, 2018. These straight-line cloud patterns are called ship tracks, and they’re formed via ships’ exhaust. This image is off the coast of Portugal, where ship traffic is high, and some of these tracks stretch hundreds of miles. The narrow ends of the clouds are youngest, while the broader, wavier ends are older. NASA explained how they form:

Some of the pollution particles generated by ships (especially sulfates) are soluble in water and serve as the seeds around which cloud droplets form. Clouds infused with ship exhaust have more and smaller droplets than unpolluted clouds. As a result, the light hitting the polluted clouds scatters in many directions, making them appear brighter and thicker than unpolluted marine clouds, which are typically seeded by larger, naturally occurring particles such as sea salt.

Deborah Byrd created the EarthSky radio series in 1991 and founded EarthSky.org in 1994. Today, she serves as Editor-in-Chief of this website. She has won a galaxy of awards from the broadcasting and science communities, including having an asteroid named 3505 Byrd in her honor. A science communicator and educator since 1976, Byrd believes in science as a force for good in the world and a vital tool for the 21st century. "Being an EarthSky editor is like hosting a big global party for cool nature-lovers," she says.